1. Field of the Invention
The present invention relates to a liquid discharging head drive device and drive method, and in particular to a drive device and drive method that drive a liquid discharging head to discharge, in accompaniment with the application of a drive signal voltage to a drive element, recording droplets from a nozzle disposed with that drive element.
2. Description of the Related Art
Conventionally, on-demand printing has been known as one type of inkjet recording method that causes ink droplets discharged from nozzles of a recording head to adhere to a recording medium to record an image of characters or photographs on the recording medium. On-demand printing is a method where ink droplets are intermittently discharged from the nozzles in correspondence to recording information. As one type of on-demand printing, the piezoelectric method is known where the displacement of piezoelectric elements accompanying the application of a drive signal voltage to those piezoelectric elements is transmitted via diaphragms to pressure chambers filled with ink, whereby pressure fluctuations inside the pressure chambers cause ink droplets to be discharged from the nozzles.
In this piezoelectric method, because pressure is added to the ink inside the pressure chambers by the piezoelectric effect of the piezoelectric elements to cause ink droplets to be discharged, when the application of the drive signal voltage to the piezoelectric elements is simply switched ON and OFF (using, as the drive signal voltage applied to the piezoelectric elements, a waveform whose voltage level changes in two stages), problems arise such as satellites and mist occurring. For this reason, in order to suppress the occurrence of satellites and mist by controlling menisci with high precision, a drive signal voltage with a complex waveform (e.g., a waveform whose voltage level changes in at least three stages) becomes necessary. As a configuration to generate such a drive signal voltage, a configuration is conceivable where waveform data defining voltage values of the drive signal voltage at each point in time are converted by a D/A converter to an analog drive signal, with the drive signal being amplified by an amplifier to generate a drive signal voltage. However, in this configuration, it is necessary to dispose numerous D/A converters and amplifiers in correspondence to the numerous piezoelectric elements disposed in the recording head. Thus, there are the problems that the cost of the drive device rises and the size of the drive device becomes large.
In relation to this, Japanese Patent Application Laid-Open Publication (JP-A) No. 2001-310461 discloses technology where the waveform of a drive signal voltage (drive pulse) is used as a waveform comprising the pulse of a first voltage V1 that enlarges the ink channels and the pulse of a second voltage V2 that causes the ink channels to shrink, and where the ratio between the first voltage V1 and the second voltage V2 in the waveform and the continuation time of each pulse are selected to enable high-speed and stable driving of the ink channels.
JP-A No. 8-281939 discloses technology where, in a one-time jetting operation, a stage where a drive signal voltage of a middle level (20V) is applied to the piezoelectric elements (initial stopped state), a stage where a drive signal voltage of a high level (100V) is applied to the piezoelectric elements (jetting stage) and a stage where the drive signal voltage applied to the piezoelectric elements is switched to a low level (0V) (state where post-jetting residual ink is sucked and removed from the nozzle surface) are disposed.
JP-A No. 2002-019107 discloses technology where plural waveform generators are disposed which generate fundamental waveform signals of drive signal voltages in accordance with a parameter signal inputted from a parameter register, and where a predetermined fundamental waveform signal is selected in accordance with a drive signal based on image information from the plural fundamental waveform signals generated by the plural waveform generators.
JP-A No. 2003-251806 discloses technology where, when driving a printing head disposed with plural actuators that drive plural printing elements, a drive waveform outputted from a drive waveform output circuit is outputted to the actuators to drive the actuators, a timing when a large current flows when the drive waveform is applied to the actuators is stored in advance with respect to the drive waveform, and the timing at which the drive waveform is applied is controlled so that times when large currents flow do not overlap between one group of actuators among the plural actuators and another different group of actuators.
In the inkjet recording method, attempts are being made to improve the quality of images recorded on the recording medium, by switching, per individual nozzle (individual piezoelectric element) and in accordance with the image to be recorded, the sizes of the dots formed on the recording medium by the ink droplets discharged from the recording head (dot diameter modulation), and by correcting, per individual piezoelectric element, variations in dot diameter resulting from variations in the characteristics of the individual piezoelectric elements disposed in the recording head (head characteristic correction). In order to realize dot diameter modulation and head characteristic correction, it is necessary to change, in accordance with the diameters of the dots to be formed on the recording medium and the characteristics of the piezoelectric elements, the waveform of the drive signal voltage applied to each piezoelectric element.
With respect to this, the technology described in JP-A No. 2001-310461 uses a waveform whose voltage level is switched in three stages as the drive signal voltage, and there is description in JP-A No. 2001-310461 in regard to selecting the ratio between the first voltage V1 and the second voltage V2 and the continuation time of each pulse; however, the specific circuit configuration for generating the drive signal voltage is not disclosed, and there is the problem that the waveform of the drive signal voltage cannot be changed to a desired waveform, such as generating a drive signal voltage of a waveform where the pulse of the first voltage V1 is added after the pulse of the first voltage V1 and the pulse of the second voltage V2.
In the technology described in JP-A No. 8-281939, the input voltage is divided by a voltage dividing circuit, where plural resistors and plural transistors are combined, to generate three types of voltage values, and the voltage value to be outputted of the three types of generated voltage values is selected by switching the transistors ON and OFF, whereby a drive signal voltage of a waveform whose voltage level is switched in three stages is generated, and it is also possible to change the waveform of the drive signal voltage to a desired waveform by switching the timing and ON and OFF pattern of the plural transistors. However, in the technology described in JP-A No. 8-281939, because it is necessary to dispose numerous voltage dividing circuits in correspondence to the piezoelectric elements in order to switch the waveform of the drive signal voltage using, as a unit, the piezoelectric elements disposed in the recording head, there is the problem that it is easy for variations to arise in the drive signal voltage applied to the piezoelectric elements due to manufacturing variations of the resistors disposed in the voltage dividing circuits. There is also the drawback that the consumption current is large because a through current flows to the voltage dividing circuits depending on the ON and OFF pattern of the plural transistors.
The technology described in JP-A No. 2002-019107 is technology that applies, to piezoelectric elements, a drive signal voltage of a waveform whose voltage level changes in two stages, and it is difficult to control menisci with high precision. Also, in the technology described in JP-A No. 2002-019107, plural types of two-value fundamental waveform signals generated by the plural waveform generators are inputted to selectors disposed in correspondence to the piezoelectric elements of the recording head, and the fundamental waveform signals selected by the selectors are amplified by drivers and applied to the piezoelectric elements as the drive signal voltage. Thus, in this configuration, in order to apply, to the piezoelectric elements, a drive signal voltage of a waveform whose voltage level changes in at least three stages, it is necessary to enable the waveform generators, which are digital circuits that handle two values and comprise a multiplexer, comparator, F/F, timer, zero detector and counter, to generate fundamental waveform signals of waveforms whose voltage level changes in at least three stages, and there is the problem that the configuration of the waveform generators becomes extremely complex.
In the technologies described in JP-A Nos. 2001-310461, 8-281933 and 2002-019107, because consideration is not given to the timing where the drive signal voltage is applied to the piezoelectric elements of the recording head, it is easy for a large current to flow when the drive signal voltages are applied at the same timing to the plural piezoelectric elements, and there is also the potential for an excessive load to act on the drive device. This problem can be solved by applying the technology described in JP-A No. 2003-251806, but with this technology, a storage circuit that stores the timing when the large current flows becomes necessary and a circuit that determines whether or not the launch timings overlap also becomes necessary, so that there is the problem that the configuration becomes complex. The drive control itself is also complex.